Various diacetylenic monomers that undergo a solid-state polymerization reaction giving rise to color development, or another visually apparent change, in a predictable and irreversible manner, have long been used as active agents in time-temperature and other ambient condition indicators. Such indicators can provide a simple visual indication of the cumulative exposure of a host product to an environmental condition. They may be used to monitor the useful shelf life of perishable host products such as a foodstuff, vaccine, medicament or the like, which can be adversely affected by inappropriate ambient temperatures or other conditions of their surroundings or storage environment. The indicator system can comprise a label incorporating the diacetylenic monomer as an active agent. The label can be affixed to the host product or to its packaging or otherwise associated with the host product, or can be embodied in some other convenient form.
In the polymerization reaction, many diacetylenic molecules are chained together to form a polydiacetylene. This reaction takes place in the solid state and is irreversible. In some cases, colorless or nearly colorless crystals of the diacetylenic compound, a monomer in this context, transform into intensely colored crystals of polymer in response to sufficient cumulative exposure to heat or another environmental condition. The polymerization reaction proceeds spontaneously, at rates largely determined by the ambient conditions.
The color change resulting from the polymerization reaction is irreversible. This property makes the compounds useful for monitoring perishable products such as food or medicines that may lose freshness after excessive cumulative exposure to heat. Diacetylenic monomers can also be employed as the active agents in indicators used for monitoring the maturity of maturing products, for example wine or cheese. For these and other purposes, the diacetylenic monomer can be incorporated as the active agent in an indicator label to be associated with a host product to be monitored. The indicator label provides a color change, derived from polymerization of the diacetylenic monomer, which can be perceived by a human viewer at a convenient viewing distance, for example by a shopper inspecting a refrigerated display in a supermarket. A reversible indicator would not be useful for these purposes.
In order to effectively track possible changes in the host product it can be desirable for the diacetylenic monomer employed to have response parameters to heat, or to another ambient condition being monitored, that may approximately correlate with the response parameters the intended host product has to the same ambient or environmental condition. For this purpose, it would be useful for the indicator formulator to have a wide range of commercially useful diacetylenic monomers providing a variety of response parameters from which to choose a suitable monomer for monitoring a particular host product.
Many polymerizable diacetylenic compounds are known or have been suggested, some of which provide useful color changes upon polymerization, see for example Patel U.S. Pat. Nos. 3,999,946; 4,189,399 and 4,384,980 and Preziosi et al. U.S. Pat. Nos. 4,789,637 and 4,788,151. However, only a limited number of these compounds exhibit performance parameters that render them useful for monitoring a perishable or maturing commercial product. The limited number of useful diacetylenic compounds that is commercially available restricts the choice of response parameters an indicator formulator has when seeking a diacetylenic monomer to use as an active indicator agent.
Accordingly, the art includes proposals for modifying the reactivity of a given commercially useful diacetylenic monomer so that it responds differently to a given ambient condition, so as to give the formulator more choices.
For example, U.S. Pat. No. 4,788,151 to Preziosi et al. discloses dissolving two or more diacetylenic compounds in a heated common solvent and recrystallizing the solvated compounds to produce a co-crystallized composition. The co-crystallized composition has a reactivity different from that of the individual compounds.
International Publication No. WO 2004/077097 to JP Laboratories discloses radiation sensitive devices, such as a film, sticker or badge for monitoring a dose of high-energy radiations utilizing radiation sensitive materials, such as diacetylenes. As described in WO 2004/077097, diacetylenes are known to crystallize into more than one crystallographic modification or phase, and by selecting a proper solvent system, some diacetylenes, can be crystallized into a phase which would have extremely low thermal reactivity and a high radiation reactivity.
Also, Prusik et al. U.S. Pat. No. 6,924,148 discloses refluxing a solution of an acetylenic agent to vary its reactivity. Some examples in the patent describe the use of glacial acetic acid and dimethyl formamide as solvents for the purpose. A number of other solvents are also disclosed as employable in the practice of the described invention. However, specific information regarding the solubilities of diacetylenic compounds in such other solvents does not appear to be provided. Some X-ray diffraction data are provided for one diacetylenic monomer compound.
Furthermore, U.S. Pat. No. 7,019,171 to Prusik et al. discloses non-comminutive processes for favorably influencing particle size in acetylenic agent crystallization processes. Some described examples employ solutions of acetylenic agents in acetic acid and various solvents such as aqueous methanol and ethyl 3-ethoxypropionate are described as useful as a precipitation or quenching fluid.
In addition, U.S. Patent Publication No. 2008/0004372 (application Ser. No. 11/427,589) to Prusik et al. discloses use of a reactivity-enhancing adjuvant to adapt the reactivity of a diacetylenic indicator agent.
Notwithstanding the various known diacetylenic monomers and methods of providing diacetylenic monomers with modified reactivities, it would be desirable to have more diacetylenic monomer reactivity options available, and to have new methods and products for providing diacetylenic monomers with new or modified reactivities.
The foregoing description of background art may include insights, discoveries, understandings or disclosures, or associations together of disclosures, that were not known to the relevant art prior to the present invention but which were provided by the invention. Some such contributions of the invention may have been specifically pointed out herein, whereas other such contributions of the invention will be apparent from their context. Merely because a document may have been cited here, no admission is made that the field of the document, which may be quite different from that of the invention, is analogous to the field or fields of the present invention.